Malibongwe Shadrach Manono

Closing water circuits and dry-stacking tailings are now central goals of sustainable mineral processing, and both depend on the efficient coagulation-flocculation-sedimentation (C-F-S) of flotation tailings in thickeners. Flotation reagents, namely, collectors, frothers, depressants and modifiers, are selected for their effect on valuable mineral grade and recovery, while thickener performance is optimised separately through coagulant and flocculant dosing; the two chemistries are rarely considered together. Yet flotation tailings entering a thickener are not chemically inert; many depressants and modifiers are polymeric or ionic species that resemble the coagulants and flocculants used downstream, and could plausibly enhance, suppress or otherwise alter particle destabilisation and floc growth. This review synthesises literature on flotation reagent chemistry, coagulation-flocculation theory, and the factors (pH, ionic strength/valence, dosage, zeta potential and temperature) known to govern C-F-S performance in both tailings and general water-treatment systems, in order to evaluate the plausibility and evidence base for this coupling. Findings from the literature show consistent qualitative agreement between flotation-tailings and water-treatment systems for each factor, but almost no direct evidence on residual flotation reagents themselves, a gap now beginning to be addressed by recent studies on residual coagulants, flocculants and dewatering aids re-entering flotation circuits. The review concludes with a focused set of research priorities rather than a detailed experimental protocol, aimed at establishing whether, and under what conditions, flotation reagent selection should be treated as a dewatering-relevant decision. Document Type: Review Cited as: Manono, M. S., Corin, K. C. Bridging flotation and dewatering chemistry: A review of flotation reagent effects on tailings coagulation-flocculation-sedimentation. Sustainable Earth Resources Communications, 2026, 2(3): 115-130. https://doi.org/10.46690/serc.2026.03.02

This research aims to explore a novel preparation and characterization of modified BFIS slag, with magnesium oxide, ammonium chloride as a hydrating agent, and the MgO/BFIS sorbent, all of which were synthesized utilizing an atmospheric hydration procedure. The sorbents were made by altering the hydration conditions, which included the MgO/BFIS slag weight ratio (1:1 to 1:4), hydration temperature (40–90 °C), ammonium chloride (1–4 g), and hydration length (4–12 h). The carbonation process was carried out using thermogravimetric analysis (TGA) at 800 °C. At all preparation conditions, the specific surface area of MgO/BFIS composite ranged between (50.2–53.6 m ² /g) and was more than that of MgO (5.34 m ² /g). The produced MgO/BFIS sorbent had a more porous structure than virgin MgO or BFIS slag, according to SEM micrographs. X-Ray Diffraction (XRD) and Fourier-Transform Infrared spectroscopy (FTIR) analysis revealed the existence of complex compounds comprising magnesium silicate hydrate in the produced sorbents. This helped to explain the large BET-specific surface area. The Brunauer–Emmett–Teller (BET) specific surface area decreased as the amount of BFIS slag increased and increased with the hydration temperature, time, and amount of hydrating agent increased. The shrinking core model was used to fit the kinetics of the carbonation reaction, and the results show that diffusion over the product layer was the rate-limiting step. Graphical Abstract

Low-grade Cu-Ni-PGM concentrators increasingly operate under the combined constraints of declining ore grades, variable process water quality, and the need to optimise reagent suites for sustainable production. This study examines the performance of mixed thiol collectors under controlled inorganic electrolyte conditions representative of modern concentrator water circuits. A comprehensive review of mixed-collector flotation is followed by a bench-scale experimental programme using sodium isobutyl xanthate (SIBX), sodium diethyl dithiophosphate (SEDTP), and their mixtures, tested in synthetic plant water and in CaCl₂ and NaCl solutions at fixed ionic strength. Results show that increasing the SEDTP molar fraction significantly enhances froth stability, water recovery, and solids recovery across all water types, driven by stronger surface activity and the presence of surface-active impurities. Ca²⁺ bearing process water promoted the highest Cu and Ni recoveries but also intensified gangue recoveries at high SEDTP levels, lowering concentrate grades. In contrast, SIBX-rich mixtures yielded superior selectivity, particularly in Na⁺ containing process water. Mechanistic interpretation shows that combined effects of electrical double-layer compression, mineral activation, mixed-collector adsorption, and froth stabilisation behaviour govern the observed grade–recovery trends. Overall, this study demonstrates that thiol-collector synergy is strongly water-chemistry-dependent, and that optimising collector mixtures requires coordinated control of reagent composition and process water quality. The findings provide a mechanistic basis for water-responsive reagent design in Cu-Ni-PGM flotation circuits.